This invention relates to generators used in land-based power generation systems and more specifically, to mechanical restraint configurations for preventing axial movement of composite material reinforcing rings used in rotor containment systems.
Certain generators manufactured by the assignee of this invention utilize carbon-epoxy (C/Ep) rings as an enclosure for restraining any radial outward movement of the copper coils and magnetic shield in a rotor assembly due to centrifugal forces during operation of the turbine. See, for example, U.S. Pat. Nos. 6,291,919 and 6,495,942. Startup and shutdown cycles combined with high frequency vibration provide sufficient energy to force the rings to move axially along an underlying magnetic shield, however, potentially covering cooling holes in the shield and creating rotor imbalance with associated bearing distress and an eventual reduction in reliability. Prior designs have utilized epoxy adhesive to secure the rings, but large differential thermal response characteristics between the C/Ep ring, epoxy adhesive and magnetic shield material (steel or nickel) have created a potentially significant problem. Specifically, if the adhesive rigidly bonds to both components, stresses due to differential thermal expansion will be sufficient to crack the adhesive, causing the ring to experience non-uniform loading with the inner diameter (loss of continuous elastic foundation) and axial movement.
Some prior designs have utilized a “slip plane” in the form of a polytetrafluoroethylene (such as Teflon®) film between the ring and epoxy adhesive, allowing the adhesive to only bond tightly to the magnetic shield material. Axial movement of the ring with respect to the adhesive was prevented by using radially oriented non-magnetic pins and/or hand-built dams of epoxy.